1. Field of the Invention
The present invention relates to a fuel injection valve for use in a fuel supply system of an internal combustion engine, and particularly to an electromagnetic type fuel injection valve that can perform promotion of atomization and suppression of dispersion of fuel spray shape in spray characteristic, and also can perform enhancement of flow rate precision and suppression of variation caused by ambient pressure variation in flow rate characteristic.
2. Description of the Related Art
Recently, exhaust gas regulation (emission limit) has been enforced to vehicles, etc., and under such a situation, it has been required to enhance atomization of fuel spray injected from a fuel injection valve. Various studies have been made on the atomization of fuel spray. For example, JP-A-2007-100515 discloses a technique of disposing a nozzle hole entrance portion inside with respect to the mainstream of fuel flow from a valve seat portion and also rapidly reducing the cavity flow passage area just above the nozzle hole to promote the fuel flow having a large plunge angle at the entrance of the nozzle hole, whereby the fuel spray is atomized while suppressing excessive fuel spray diffusion.
Furthermore, JP-A-2004-137931 discloses a technique of designing the orifice of an orifice plate so that the orifice length at the outside in the radial direction is shorter than the orifice length at the inside in the radial direction with respect to the axial center X of the fuel injection valve, thereby performing atomization of fuel injection with a simple structure.
FIG. 1 is a cross-sectional view showing the overall construction of a general fuel injection valve 1, and it is constructed by a solenoid device 2, a housing 3 serving as a yoke portion of a magnetic circuit, a core 4 as a fixed iron core portion of the magnetic circuit, a coil 5, an armature 6 as a movable iron core portion of the magnetic circuit, and a valve device 7. The valve device 7 is constructed by a valve plug 8, a valve main body 9 and a valve seat 10. The valve main body 9 is pressed and fitted around the outer-diameter portion (outer peripheral portion) of the core 4 and welded. The armature 6 is pressed and fitted into the valve plug 8, and then welded. The fuel spray plate 11 is inserted into the valve main body 9 under the state that the fuel spray plate 11 is bonded to the downstream side of the valve seat at a welding portion 11a, and then bonded to the valve seat 10 at a welding portion 11b. Plural fuel orifices 12 penetrating through the plate thickness direction are formed in the fuel spray plate 11 by press forming.
FIGS. 8 to 11 are detailed cross-sectional views of the tip portion of a fuel injection valve, which particularly correspond to FIG. 5 of JP-A-2007-100515. Next, the operation of the fuel injection valve will be described with reference to FIG. 1 as well as FIGS. 8 to 11.
When an operation signal is transmitted from a control device (not shown) for an engine to the driving circuit of the fuel injection valve 1, current is made to flow through the coil 5, and a magnetic flux occurs in the magnetic circuit comprising the armature 6, the core 4, the housing 3 and the valve main body 9. The armature 6 is operated to be attracted to the core 4 side, and the valve plug 8 which is designed integrally with the armature 6 is separated from the valve seat face 10a, whereby a gap 17a is formed.
At this time, fuel is passed from a chamfered portion 13a of a ball 13 welded to the and portion of the valve plug 8 through the gap between the valve seat face 10a and the valve plug 8, and injected from plural orifices 12 into an engine intake pipe. Subsequently, when an operation stop signal is transmitted from the control device of the engine to the driving circuit of the fuel injection valve, supply of current to the coil 5 is stopped, and the magnetic flux in the magnetic circuit is reduced, so that the gap 17a between the tip portion 13 of the valve plug and the valve seat face 10a is closed by a compression spring 14 which presses the valve plug 18 in a valve closing direction, whereby the fuel injection is finished. The valve plug 8 slides along a guide portion of the valve main body 9 at a side surface 6a of the armature 6, and under a valve open state, an upper surface 6b of the armature 6 abuts against the lower surface of the core 4.
In the system of JP-A-2007-100515, a projecting portion 11d projecting to the downstream side is provided at the center portion of the orifice plate, and the orifice plate 11 is disposed so that a virtual circular conical surface 10b extending to the downstream side of the valve seat surface 10a and an orifice arrangement surface 11c at the outer peripheral side of the projecting portion intersect to each other to form one virtual circle 15 (see FIG. 9). Therefore, fuel flowing along the sheet surface 10a plunges into the orifice entrance portion 12a, and then pressed against the inner wall 12e of the orifice, whereby the fuel flow is converted to fuel flow 16d (see FIG. 10) along the curvature of the orifice. At this time, the optimum orifice length is required to form falcate liquid film in the orifice. If the length is excessively long, the fuel goes round in the orifice and thus becomes a string of sprayed fuel. If the length is excessively short, the fuel flow is not sufficiently converted to the flow along the curvature of the orifice, so that not only the fuel becomes a string of sprayed fuel, but also the actual injection angle of the fuel is smaller than a desired injection angle.
Furthermore, in the cross-section passing through the axial center 13e of the valve plug and the center of the orifice, the distance between a first parallel line 18a parallel to the valve seat face 10a passing through the inside 12c in the radial direction of the axial center X of the fuel injection valve of the orifice entrance portion 12a and a second parallel line 18b parallel to the valve seat face 10a passing through the outside 12d in the radial direction of the fuel hole entrance portion is maximum when the angle θ between the valve seat face 10a and the plane 11c on which the orifice is disposed is equal to 90°, and also is minimum when the angle concerned is equal to 0°.
In the structure disclosed in JP-A-2007-100515 (prior art 1), the orifice entrance portion 12a is disposed on the plane 11c perpendicular to the axial center of the valve plug, and thus the intersecting angle θ between the valve seat face 10a and the orifice arrangement plane 11c is large, and the distance between the parallel lines described above is large. Therefore, the distance to the exit of the orifice is different between the fuel impinging against the inside 12c in the radial direction of the center axis X of the fuel injection valve of the orifice entrance portion 12a and the fuel which passes through the outside 12d in the radial direction of the orifice entrance portion 12a and impinges against the inside 12e in the radial direction of the axial center X of the fuel injection valve of the orifice wall. Therefore, the orifice length which is optimum to atomization with respect to both the fuels does not exist in the structure concerned.
Particularly, there is a case where not increase of the number of orifices, but increase of the orifice diameter is required from the viewpoint of the layout performance of the orifice particularly in order to apply the fuel injection valve to a large flow-rate specification. In this case, the distance between the inside 12c and outside 12d in the radial direction of the axial center X of the fuel injection valve at the orifice entrance portion 12a is large due to the increase of the orifice diameter, and thus the particle size of the atomized fuel deteriorates. Furthermore, in order to implement a large injection angle, it is required to increase the inclination angle of the orifice. In this case, the flatness rate of the shape of the orifice entrance is increased, so that the distance between the inside 12c and outside 12d in the radial direction of the axial center X of the fuel injection valve at the orifice entrance portion 12a is increased, and thus there is a problem that the particle size of the atomized fuel deteriorates.
FIGS. 12 to 15 are detailed cross-sectional views of the tip portion of the fuel injection valve disclosed in JP-A-2004-137931 (prior art), and the operation of the fuel injection valve will be described with reference to FIG. 1 as well as FIGS. 12 to 15.
In this type of fuel injection valve, the orifice of the orifice plate is designed so that the orifice length at the outside in the radial direction is shorter than the orifice length at the inside in the radial direction with respect to the center axis X of the fuel injection valve. However, the upstream end face 11c of the orifice plate 11 is planar, and thus in the fuel flow, mainstreams 16a and 16b passing through the gap between the valve plug 8 and the valve seat 10 and advancing toward the orifice and a radial U-turn stream 16c passing through the orifices and turning around due to counter flow at the center of the orifice plate crash head-on just above the orifice, and the main streams are decelerated.
When the main stream is decelerated as described above, the force of pressing fuel against the inner wall 12e at the inside in the radial direction of the axial center X of the fuel injection valve of the orifice is weakened, and the thickness of the liquid film formed inside the orifice is larger, so that atomization deteriorates. Furthermore, when turbulence is generated in the fuel flow, there is obtained an effect of promoting disruption of the liquid film of fuel injected from the orifice by the energy of the turbulence. However, droplets which are once separated from the liquid film and formed are difficult to be further disrupted due to the effect of the surface tension.
Therefore, in the system of atomizing fuel spray by forming falcate liquid film in the orifice, it has been proved from a fuel spray observation result that atomization is more promoted by disrupting liquid film after the liquid film injected in a falcate shape from the orifice spreads and thus the liquid film is thinner, and it is more advantageous in atomization to reduce the turbulence in the fuel flow.
As described above, the fuel injection disclosed in JP-A-2004-137931 has a problem that the particle size of fuel spray deteriorates because turbulence occurs in the fuel flow at the orifice entrance portion due to the frontal crash.
With respect to the problems, a structure obtained by combining a concave portion disclosed in JP-A-2004-137931 with the technique disclosed in JP-A-2007-100515 as shown in FIGS. 16 to 19 is an effective method of respectively optimizing the distance to the orifice exist with respect to the fuel which impinges against the inside 12c in the radial direction of the axial center X of the fuel injection valve of the orifice entrance portion 12a, and the distance to the orifice exit with respect to the fuel which passes through the outside 12d in the radial direction of the orifice entrance portion 12a and impinges against the inside 12e in the radial direction of the axial center X of the fuel injection valve of the orifice wall. However, this method has the following problem in mass productivity.
That is, with respect to the processing of the orifice plate, a method of successively processing a strip-shaped plate member called as hoop material by press working which is excellent in processing cost and processing precision is used as a method best in cost and quality in consideration of mass productivity. In the case of a symmetrical two-spray type fuel injection valve adapted to a single cylinder or two-valve engine, the shape of the orifice is also symmetrical. Therefore, in order to reduce the metal mold cost, enhance the quality and promote the space efficiency of a factory, a hoop material is reeled off after the orifices at one side are processed, and then the orifices at the opposite side are processed by using the same metal mold.
Furthermore, a burr removing step and a cleaning step after the orifice processing, a step of cutting out a plate from the hoop material, etc. are provided in addition to the orifice processing. If the respective steps are linked to one another on a line, the space efficiency of the factor deteriorates, and there are cumbersome problems of product inspection in every step, a treatment to processing failure, etc. Furthermore, since the respective steps are made independent of one another, except for the final step of cutting out the plate from the hoop material, the hoop material is reeled off every step. In the structure that a projecting portion is provided at the center portion of the orifice plate as in the case of the technique disclosed in JP-A-2007-100515, it is impossible to carry out the reel-off of the hoop material after the projecting portion is formed because the projecting portion and the plate interfere with each other. Therefore, the formation of the projecting portion at the center portion of the orifice plate is required to be carried out just before the final step of cutting out the plate from hoop material.
In the structure that the concave portion disclosed in JP-A-2004-137931 is combined with the technique disclosed in JP-A-2007-100515 as shown in FIGS. 16 to 19, the formation of the concave portion is required to be executed before the orifice processing in consideration of deformation of the orifices, and all the steps are shown in FIG. 20. In FIG. 20, reference numeral 50 represents the hoop material, and reference numeral 60 represents pilot pin guides. The concave portion corresponding to each orifice in step 1 is formed by forge-formation, for example. In step 2, the orifice processing (one side) is executed by press blanking. In step 3, the orifice processing (opposite side) is executed by press blanking. After the orifice processing, burr is removed by brush machining, for example, and then cleaning is executed.
Subsequently, in step 4, the projecting portion at the center portion of the plate is formed by stretch forming. In the final step 5, the orifice plate is cut out by press blanking, drawing or the like. It is needless to say that the movement between the respective steps is performed by reeling off the hoop material 100. FIGS. 21A and 21B are enlarged views of the detailed structure of the orifice plate in the stretch forming step, wherein FIG. 21A shows a state before the stretch forming step, and FIG. 21B shows a state during the stretch forming step. In FIGS. 21A and 21B, reference numeral 70 represents a punch, reference numeral 71 represents a punch guide, reference numeral 80 represents a dice, reference numeral 81 represents a dice guide, reference numeral 11 represents the orifice plate, and reference numeral 320 represents the concave portion.
In FIG. 21A, Y represents a deformed portion (boss portion) which is formed on the end face at the upstream side of the plate when the concave portion 20 is formed on the end face at the downstream side of the orifice plate 11. The dice guide 81 is disposed at both the sides of the dice 80 serving as a stretch forming mold for the orifice plate, and the orifice plate 11 having the concave portion corresponding to each orifice formed therein is mounted on the dice guide 81. Subsequently, the punch guide 71 strokes to pinch the outer peripheral portion of the orifice plate 11.
At this time, a gap G occurs between the plate 11 and the punch guide 71 due to the deformed portion Y of the end face at the upstream side of the plate. Accordingly, in the subsequent stretch forming step of the projecting portion at the center portion of the orifice plate, the punch 70 strokes, and the formation of the projecting portion at the center portion of the orifice plate is started as shown in FIG. 21B. At this time, it is impossible to sufficiently press the orifice plate by the metal mold due to existence of the gap G, and thus drawing is executed. Accordingly, there is a problem that a deformed portion Z is formed in the orifice around the projecting portion in FIG. 21B.
In order to solve the problem of the deformation of the orifices, it is required to form the projecting portion before the orifice processing or the step of forming the concave portion corresponding to each orifice. However, as described above with reference to FIG. 20, it is impossible to reel off the hoop material after the projecting portion is formed, and thus it is required to link the respective steps on a line. Therefore, there is a problem in cost and quality management.